Creepers are produced by the Thorian, appearing as corpse-like humanoids with long claws and no noticeable eyes.

Creepers hibernate (sitting down and curling up) until approached, then rise up at the Thorian's command to use melee attacks or vomit green acid onto their enemies, causing massive toxic damage that ignores shields. They are mostly found down in the Thorian's lair, though a few come above ground at Zhu's Hope to protect the freighter.

Commander Shepard encounters more Thorian Creepers on Nodacrux, shipped there from Feros for study. According to the scientists there, they found a way to turn the Creepers into a docile source of labour, but when the Thorian died the Creepers went berserk and began attacking. ExoGeni Corporation also sent a group of Thorian Creepers to Cerberus.

Thorian Creepers will first hibernate until disturbed or until the Thorian is threatened (while hibernating, they are invulnerable to any attack). Once 'awakened' they will race toward the squad, use their acid attack, and then slash at the party for melee damage. They tend to be extremely resistant to gunfire and can take a lot of slugs without slowing down.

They are also vulnerable to biotics: Lift or Throw, especially in a confined space, will crush them against walls and cause heavy damage, and Warp will make gunfire more effective. Throw is also highly effective on the Creepers in the underground portions of the Thorian's lair, as it is easy to knock them off high ledges so they fall to their death. Because Creepers are comparatively light compared with other foes, Throw will also launch them back much further.

Singularity is useful when they're clustered in groups, lifting all enemies within its radius into the air.

There are two easy ways to kill a Thorian Creeper. One is to use an anti-Thorian gas grenade, which will result in an instant kill. The other is to approach one of the Thorian's neural nodes, and use Marksman or a sniper rifle to attack the node from a distance. While doing this will rouse the Thorian Creepers around it and make them attack, destroying the node will also cause all the Creepers which were guarding it to die.

Although Thorian Creepers are physiologically robust, they wear no armour. This means that they are extremely vulnerable to melee attacks. A Creeper will stand still for a brief period before using its acid spit attack, and they can be struck at this moment to knock them over. Although melee attacks inflict little damage against Creepers, they are almost guaranteed to knock the target flat, even on the highest difficulty settings. It is also possible to knock down multiple Creepers with one blow, allowing the squad to attack them with impunity. Being biological enemies, they are also vulnerable to Shredder Ammunition and Neural Shock. Because their attacks bypass shields, armor upgrades that increase damage protection or health regeneration are an excellent choice.